The invention relates to an apparatus for the acquisition of the surface shape of a distant object by means of picture element scanning with at least one optomechanical scanner which moves relative to the surface of the object.
Such an apparatus is disclosed in Bildmessung und Luftbildwesen, 51 (1983), part 3, pages 103 to 117, which is concerned with plotting the earth's surface from aircraft or satellites. Pages 112 ff of this text describes an optomechanical scanner composed substantially of a lens, a radiation detector arranged in the focal plane of the latter, as well as a rotatable optical element located in front of the lens toward the object. The optical element is in the form of a reflector swiveling about a rotational axis parallel to the flight direction with its reflector surface inclined relative to the latter. The radiation detector is arranged along the optical axis of the lens on its image side. Its "viewing" direction extends along the optical axis toward the object up to the reflector surface of the swiveling reflector. A motor rotates the latter so that the viewing direction periodically and repeatedly swivels transversely relative to the flight direction. As a result, surface elements of the earth's surface are imaged one after the other in successive scanning traces on the radiation detector. The latter can thus measure the corresponding radiation values. Such an apparatus cannot acquire data concerning the three-dimensional surface shape of a distant object, in this case the earth's surface.
Such a spatial acquisition is possible, however, with apparatuses and methods which are described in DE-PS 29 40 741, DE-PS 30 43 577 and DE-OS 32 19 032. These apparatuses make it possible to scan an object, e.g. a portion of terrain, with a trilinear scanning camera, to access the three-dimensional shape of the object and to determine the orientation parameters of the camera (position and angle of inclination) along the relative movement between the scanner and the object.
In this case, high-resolution, rectilinear semiconductor sensors such as CCD-sensors are provided for the scanning. The semiconductors sensors contain a multiplicity of individual radiation detectors in a sensor line in each instance. The apparatus scans the entire line simultaneously in each instance with a line cycle or integration interval according to the so-called "push-broom principle". Three linear semiconductor sensors are arranged transversely relative to the flight direction. The device and its respective evaluating method are designated in the literature, as well as the following as the DPS-evaluating method (DPS=digital photogrammetry system). Principles of the DPS-evaluating method are described, for example, in Photogrammetric Engineering and Remote Sensing, vol. 50, No. 8, August 1984, pages 1135 to 1142. The method is based on the scanning of an object with a trilinear scanner in which three linear sensor lines arranged in the focal plane of a camera at a given distance from one another and transverse relative to the flight direction, scan the object line-by-line from different viewing angles and accordingly produce three picture strips of various perspectives. Evaluation involves first determining the homologous, image points of the same object point in these three image strips and the respective three picture taking times and the assigned picture coordinates to correlation. After that an analytical evaluating process determines the orientation parameters of the camera along the flight path, as well as the three-dimensional object coordinates of the correlated picture elements.
The DPS system, particularly its evaluating method, is distinguished by the three sensor lines arranged in the focal plane of the camera forming a planar central perspective in each instance, with the objective as a center point and the respective scanning trace in the terrain to the time t of the line scan that simultaneously detects the picture elements of the three entire lines. This planar center perspective is a prerequisite, and is taken as the basis of the evaluating method of the DPS system. Therefore, it could previously not be assumed that this evaluating method could also be used without meeting the prerequisite of the planar center perspective.
The CCD sensors used in the DPS system are usually sensitive in the spectral region of 0.4 .mu.m to 1 .mu.m. Productions of such sensors for other wavelengths, for example, the infrared region or even microwaves encounters considerable technical difficulties or is impossible. The use of the DPS method is therefore practically limited to the wavelength region of 0.4 .mu.m to 1 .mu.m because of the limited spectral region of CCD sensors. Therefore, three-dimensional acquisition of the object surface was also previously possible only in this wavelength region. For other spectral regions, particularly the infrared region, the aforementioned optomechanical scanner was used, but a three-dimensional acquisition of the object surface was not attainable in this manner.